The present invention relates to a charge-removing device for eliminating the electrostatic charge liable to be carried on thin dielectrics strip, in particular those of the rolled film type which are used as image transfer ribbons in electrostatic printers.
These dielectric strips have the property of being easily electrified when they come into contact with other materials or with themselves during forming.
Such electrification sometimes generates large parasitic electric fields capable of disturbing the operation of the apparatus using the strips.
Parasitic electric fields created in this way originate from the electrostatic charges carried on the surface of the dielectric in active dipoles which are created by the molecular chains of the materials constituting the dielectric, and they also originate to a smaller extent from surface doublets.
In some applications, and in particular in electrostatic printing, means are thus provided for eliminating the electrostatic charges carried by the thin dielectric strip before use, i.e. while it is being unwound if it is in the form of a film stored on a reel.
The commonest method of eliminating electrostatic charge consists in rubbing a suitably connected conductive assembly of the brush or ruffle type over the dielectric surface to be discharged. Such conductive assemblies are suitable for preventing the electric field from reaching too high a value, but they are not capable of removing it completely.
Another known method consists in holding a small diameter metal wire taut and parallel to the surface of the dielectric and in subjecting it to high voltage AC which ionizes the ambient air to create a flow of alternatively positive and then negative ions which compensate the surface charge on one of the two faces of the dielectric by electrostatic attraction.
However, this method is difficult to implement since the electrode-forming wire must be free from surface state defects and free of impurities, and must be accurately placed relative to the film which is conventionally the moving part, since otherwise charge is not removed uniformly.
Consequently, the present invention proposes a charge-removing device for eliminating electrostatic charge on a thin dielectric strip.